A. Field of Invention
The dependable and accurate cutting of moving and continuous lengths of filament bundles, film ribbons, filamentary tapes or other materials in strip-like form is a challenging and difficult problem, particularly so when the ribbon thickness or the diameter of the filaments is only a few microns.
Such materials have no appreciable stiffness and must be conveyed and aligned by a moving stream of air, feed rolls or other mechanical means or by air jets, or a combination of these, to the cutting location, where it is cut into discrete lengths, the length being determined by dividing the material transport speed by the number of cuts/minute. Fixing these two parameters when cutting filaments, into staple or flock, or ribbons will result in the desirable, uniform length product.
In scrap recovery or disposal systems, where uniform cut length is of little concern, cutting speed is normally fixed but cut length will vary with the changing speed of the process and a random length product results.
B. Description of the Related Art
Various approaches to uniform cutting of such fibers or film have been described in the prior art. U.S. Pat. No. 3,119,294 issued Jan. 28, 1964 describes a cutting apparatus in which counter-rotating rolls feed a filamentary material into an air nozzle which terminates at a stationary bed knife. A mating blade mounted on a rapidly rotating shaft cuts the filamentary material as it exits the air nozzle. See column 2, lines 23-32 and FIG. 1. This patent describes an elaborate mechanism to maintain a uniform distance between rotating cutting blade and stationery bed knife. Satisfactory cutting of the feed filaments or ribbon requires that the distance between these two elements be only a fraction of the diameter of the filaments or of the ribbon to be cut. Maintenance of this distance insures a uniform length of the cut filamentary material and long life for the cutting blades (column 4, lines 17-21). That mechanism, however, is a very complex piece of machinery with expensive precision parts that are costly and requires substantial expertise to adjust.
U.S. Pat. No. 3,831,482 issued Aug. 27, 1974 discloses an apparatus for cutting fiber into staple fiber strands. It consists of a rotating two-part disc with discardable knife blades clamped between the disc halves. The stated advantage of this arrangement is that it “eliminates the need for a removal and replacement of knives for re-grinding” (Column 2, lines 33-36). There is no disclosure of means for adjusting the length of cut fibers or apparatus associated with the cutting blades to adjust the length of the cut fiber.
Another approach to cutting filamentary material is illustrated in commonly assigned U.S. Pat. Nos. 5,450,777 and 5,836,225. These patents describe apparatus for cutting lengthy continuous tows of fiber into short, chopped fiber. This goal is accomplished by feeding multiple tows into a venturi tube which pulls the tows by negative pressure toward a cutter at the outlet of the tube. The cutter mechanism has one or more blades mounted to a high-speed drive shaft which operate in a plane transverse to the direction of movement of the tow. As the blades rotate near a cutter plate at the exit of the venturi tube, the tow fibers are cut into uniform lengths as the blade passes across the cutter plate. The cross sectional area of the cutter plate opening is such that it is momentarily covered (blocked) by the cutting blade as it rotates across the plate (See FIG. 8 of '225 patent). This arrangement tends to create a lot of high frequency noise as the air stream exiting the venture tube is repeatedly interrupted.
A similar approach to cutting filamentary material is described in U.S. Pat. No. 4,188,845 issued Feb. 19, 1980. In this arrangement, the material to be cut includes foils, plastic webs, etc., (See column 1, lines 7-9) and textile strips (See column 2, line 61). This material enters a funnel mounted atop a stationary cutting plate at the narrow end of the funnel. It proceeds through the funnel by gravity without assistance of the venturi effect described above. Rotating beneath the stationary cutting plate are multiple knife edges mounted vertically (in the plane of the foil or fiber flow) on a disc rotating below the stationary cutting plate. The knife edges are preferably adjustable to insure sliding engagement of the knife edges over the cutting plate, which is also adjustable.
Yet another approach to cutting fiber into fixed lengths for use as reinforcement in, for example, roofing shingles, is illustrated and described in U.S. Pat. No. 6,182,332 B1 issued Feb. 6, 2001. In this patent, several rotating discs with sharp edges are moved in orbit relative to a second member such as a ring with an internal track. The fiber to be cut passes between the sharp edges of the disc and internal track where it is cut. The length of the fiber to be cut is determined by adjusting the rate at which the continuous fibers are fed to the cutters and the speed at which the cutting discs are moved in orbit within the internal track (column 5, lines 23-35).